Disc molding apparatus for hubless optical disc having low radial runout

ABSTRACT

A disc molding apparatus for forming an optical disc. The apparatus has a disc substrate cavity and a sprue mechanism in fluid communication with the cavity. A removable stamper located on one side of the disc substrate cavity forms data onto the disc substrate and the stamper is relasibly locked within the apparatus by an inner holder, which includes a locking mechanism. The apparatus also has a mechanism that forms a disc alignment mechanism in the disc substrate wherein the disc alignment mechanism is between the formatted data and a center of the disc substrate and the concentricity of the formatted data is specified relative to the disc alignment mechanism.

This is a divisional of application Ser. No. 08/839,933 filed on Apr.17, 1997 now U.S. Pat. No. 6,002,663.

TECHNICAL FIELD

The present invention relates generally to the field of optical datadiscs, and in particular, to a hubless optical disc having a low radialrunout error and method of manufacturing such a disc.

BACKGROUND OF THE INVENTION

Optical data discs are a popular media choice for the distribution,storage and accessing of large volumes of data. This includes audio andvideo program material, as well as computer programs and data. Formatsof optical data discs include audio CD (compact disc), CD-R(CD-readable), CD-ROM (CD-read only memory), DVD (digital versatile discor digital video disc) media, DVD-RAM (random access memory), varioustypes of rewritable media, such as magneto-optical (MO) discs, and phasechange optical discs. In general, optical discs (such as CD-ROMs) areproduced by making a master which has physical features representing thedata formed in or on a reference surface therein. The master is used tomake a stamper, which, in turn, is used to make production quantities ofreplica discs, each containing the data and tracking information whichwas formed in the master. The high data capacity, convenience, andrelatively low production costs of such discs have contributed to theirgreat success and acceptance in the marketplace.

In optical discs, data is stored as a series of lower reflectance “pits”embossed within a plane of higher reflectance “lands”. The microscopicpits are formed on the surface of the plastic disc when the material isinjected into a mold. Typically, the pitted side of the disc is thencoated with a reflectance layer, such as a thin layer of aluminum, andin the case of a CD, followed by a protective layer of lacquer. The pitson an optical disc can be arranged in a spiral track originating at thedisc center hub and ending at the disc outer rim. The data can also liein a series of concentric tracks spaced radially from the center hub.

To read the data on an optical disc, an optical disc player shines asmall spot of laser light through the disc substrate onto the data layeras the disc rotates. The intensity of the light reflected from thedisc's surface varies according to the presence (or absence) of pitsalong the information track. When a pit lies directly underneath the“readout” spot, much less light is reflected from the disc than when thespot is over a flat part of the track. A photodetector and otherelectronics inside the player translate this variation into the 0s and1s of the digital code representing the stored information.

As optical disc technology has evolved, optical discs have increased instorage capacity. Higher density discs have resulted in the storage of agreater amount of information within the same size of disc area. Forexample, a CD having a storage capacity of 0.65 gigabytes has data pitswhich are 0.83 μm long and has a track pitch (the distance between datatracks) of approximately 1.6 μm. In comparison, a DVD disc data pit isas small as 0.4 μm long, and a track pitch of only 0.74 μm, resulting ina storage capacity of 5 gigabytes on a single layer. Similarly, MO andphase change disc track pitch varies with the density or storagecapacity of the disc.

To read high capacity optical discs having smaller pits and a smallertrack pitch, the optical disc player's read beam must achieve a smallerspot focus. Further, data must be more precisely located on the opticaldisc substrate. Ideally, the data tracks are concentrically locatedabout the center hole of the disc. During the optical disc manufacturingprocess, a centering error is introduced into the radial positioning ofthe data tracks (or track cycles) on the optical disc. This error isknown as radial total indicated runout (RTIR). RTIR is defined as themeasure of non-concentricity of the data tracks to the drive spindle onthe optical disc player.

In a conventional optical disc manufacturing process, RTIR error isintroduced during the injection molding process. The injection moldingprocess begins with a tooling mechanism. The optical tooling mechanismincludes a fixed side and a moving side. The moving side typicallyincludes a stamper for replicating data and format information into thedisc substrate, and a movable gate cut for cutting a central opening inthese disc substrates. The stamper is located by an inner holder,wherein the inner holder fits over the stamper. Several more parts arelocated at the center inside diameters of the tool. In typical opticaltooling, all of these parts need to remain concentric between the gatecut and the removable inner holder for concentric registration (orcentering) of the format information in the disc substrate relative tothe central opening or central hole.

In a disc molding process, a resin, typically polycarbonate, is forcedin through a sprue channel into a substrate cavity within the opticaltooling (mold) to form the optical disc substrate. The format of thegrooves and pits are replicated in the substrate by the stamper as thecavity is filled. After filling, the gate cut is brought forward to cuta center hole in the optical disc. After the part has sufficientlycooled, the optical tooling mold is opened and the sprue and producteject are brought forward for ejecting the formed optical disc off ofthe stamper. The inner holder may be removed to allow change out of thestamper.

Any misalignment of the aforementioned optical tooling results in thereplication of greater RTIR error in the molded disc. Further, anydebris, flash or other imperfections resulting from the gate cut action,and any misalignment of the moving stamper relative to the fixed side ofthe optical tooling will add to the RTIR error. When track pitch islarger, such as in CD optical discs, the disc reader will read CDoptical discs having typical RTIR errors between 50 and 100 μm due to arelatively large track pitch (1.6 μm). For higher capacity discs, suchas DVD discs, it is difficult (or impossible) for an optical reader toread a DVD optical disc having an RTIR error greater than 50 μm, due tothe smaller track pitch. Similar problems exist with MO disc technologyhaving a typical RTIR between 20 and 30 μm.

In order to reduce the RTIR error to acceptable (or readable) levels,hubs are installed within the center opening of the optical disc. A newcenter is located, and the hub is installed centered on the discrelative to the formatted data tracks. This is typically accomplishedusing a costly centering process. Further, the hub itself is insertmolded, resulting in a high expense relative to the total disc cost.

It is desirable to have a high density optical disc having a low RTIRerror which does not require the use of a hub for centering the drive tothe information on the disc. It is desirable to have a high densityoptical disc which may be mounted and centered on features molded intothe plastic substrate of the disc. Further, it is desirable to have adisc molding process for forming high capacity optical discs which mayinclude simple modifications to conventional optical tooling, and whichintroduces low RTIR error into the disc substrate.

SUMMARY OF THE INVENTION

The present invention includes a high-capacity optical disc having a lowRTIR error and which does not require the use of a hub for centering theinformation on the disc. The present invention also includes a discmolding process for forming high capacity optical discs which includesoptical tooling which introduces low RTIR error into the disc substrate.

In one embodiment, the present invention includes a hubless optical discfor storage of information therein. The optical disc includes a discsubstrate having a formatted surface and a central portion, wherein theformatted surface includes a plurality of generally concentric tracks,and wherein each track can be defined as a concentric ring or a cycle ofa spiral track, and wherein the central portion is proximate the centerof the disc substrate, and the formatted surface surrounds the centralportion. A disc alignment mechanism is located within the centralportion, such that the concentric registration of the formattedinformation is specified relative to the disc alignment mechanism. Thedisc alignment mechanism may be integrally molded within the discsubstrate or formed separate from the disc substrate and coupled to thedisc substrate.

The disc alignment mechanism may be matable with an optical disc playerdrive spindle. The disc alignment mechanism may include an annulargroove in the disc substrate, an annular ridge extending from the discsubstrate, or a plurality of holes in the disc substrate. The opticaldisc may further include a central hole within the disc substrate,wherein the central hole extends through the central portion of the discsubstrate. The optical disc may further include means for aiding andcoupling the optical disc to an optical disc player drive spindle,wherein the means for coupling is secured across the opening.

In another embodiment, the present invention includes a hubless opticaldisc capable of storage of a high capacity of information, the hublessoptical disc having a low radial total indicated runout error. Thehubless optical disc includes a generally disc shaped substrate having acentral hole. The disc substrate includes a formatted information areain a central portion, wherein the central portion is located between thecentral hole and the formatted disc substrate. Means are located withinthe central portion for concentric registration of the formattedinformation, including a disc alignment mechanism, wherein theconcentric registration of the formatted information is specifiedrelative to the disc alignment mechanism.

The means for concentric registration of the formatted information maybe matable with an optical disc player drive spindle. The means forconcentric registration may be integrally molded within the discsubstrate or formed separate from the disc substrate and coupled to thedisc substrate. The disc alignment mechanism may include an annulargroove in the disc substrate, an annular ridge extending from the discsubstrate, or a plurality of holes in the disc substrate. The opticaldisc may further comprise means for aiding and coupling the optical discto an optical disc player drive spindle, wherein the means for couplingis secured across the opening.

In another embodiment, the present invention includes an optical disccapable of storage of a high capacity of information. The optical discincludes a disc substrate. A formatted surface is located within thedisc substrate capable of containing data therein. The formatted surfaceincludes a plurality of data tracks, the formatted surface having atrack pitch of less than 0.74 μm, and a low radial total indicatedrunout error of less than 50 μm.

It is recognized that the formatted surface may have a track pitch ofless than 0.74 μm and a radial total indicated runout error of less than30 μm. In one preferred embodiment, the track pitch is 0.37 μm or less.

Each data track may be defined as a cycle of a continuous spiral track,or each data track may be defined as a concentric track. The disc mayhave a capacity of greater than 20 gigabytes.

The disc substrate may include a disc alignment mechanism, wherein theconcentric registration of the formatted information is specifiedrelative to the disc alignment mechanism. The optical disc may include acentral portion located between the center of the disc and the formattedsurface, wherein the disc alignment mechanism is located within thecentral portion.

In another embodiment, the present invention includes a hubless opticalstorage system, including an optical disc drive and an optical mediahaving a low radial total indicated runout. The optical media includes adisc substrate having a formatted surface in the central portion,wherein the central portion is proximate the center of the discsubstrate and the formatted surface surrounds the central portion. Adisc alignment mechanism is located within the central portion such thatthe concentric registration of the formatted information is specifiedrelative to the disc alignment mechanism. The drive comprises a drivespindle having a mating mechanism for mating the drive with the opticalmedia, the mating mechanism including a coupling mechanism formed on thedrive spindle capable of mating with the disc alignment mechanism.

The disc alignment mechanism may include an annular ridge, and thecoupling mechanism may include an annular groove capable of receivingthe annular ridge. Alternatively, the coupling mechanism may include anannular ridge, and the disc alignment mechanism may include an annulargroove capable of receiving the annular ridge.

The optical storage system may further include a mechanical hold-down,wherein the disc substrate is interposed between the drive spindle andthe mechanical hold-down. The mechanical hold-down may apply a forcenormal to the disc substrate. Means are provided which are coupled tothe mechanical hold-down for applying a force normal to the discsubstrate. In one embodiment, the force is an electromagnetic force. Theoptical storage system may further include a vacuum mechanism for urgingthe disc substrate towards the drive spindle. The vacuum mechanism mayinclude an opening in the drive spindle.

In another embodiment, the present invention includes a disc moldingapparatus for forming an optical disc in a disc molding process. Thedisc molding apparatus includes a disc substrate cavity for forming adisc substrate therein. A sprue mechanism can be in fluid communicationwith the disc substrate cavity for allowing disc material to enter thedisc substrate cavity. A removable stamper may be located on one side ofthe disc substrate cavity for forming formatted data into the discsubstrate. Means may be provided for forming a disc alignment mechanismin the disc substrate, wherein the concentricity of the formatted datais specified relative to the disc alignment mechanism.

The means for forming a disc alignment mechanism may include an innerholder. The inner holder may be releasibly mounted adjacent the stamperfor releasibly locking the stamper within the disc molding apparatus.

The inner holder may include a shape imparting mechanism for stampingthe disc alignment mechanism into the disc substrate. The shapeimparting mechanism may include an annular ring thereon, an annulardepression located therein, or a plurality of registration pinsextending therefrom. In one embodiment, the shape imparting mechanismalso releasably locks the stamper within the disc molding apparatus. Itis also recognized that the shape imparting mechanism may be located onthe stamper or other disc molding apparatus part.

In another embodiment, the present invention includes a drive spindlefor use in an optical disc drive assembly. The drive spindle includes agenerally cylindrical shaped body. Means are coupled to the generallycylindrical shaped body for engaging an optical disc. The means forengaging having a mating mechanism, wherein the optical disc includes aformatted surface and a disc alignment mechanism. The concentricity ofthe formatted surface is specified relative to the disc alignmentmechanism. The mating mechanism is engageable with the disc alignmentmechanism.

A central hub may extend from the generally cylindrical shaped body forextending through a center opening in the optical disc. A flange mayextend from the generally cylindrical shaped body, wherein the means forengaging an optical disc is coupled to the flange. The means forengaging may be formed integral the generally cylindrical shaped body.In one embodiment, the means for engaging may include an annular ringformed thereon, an annular groove formed therein, or a plurality of pinsextending therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects of the present invention and many of the attendantadvantages of the present invention will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, in which like reference numerals designate like partsthroughout the figures thereof, and wherein:

FIG. 1 is a plan view of an optical disc in accordance with the presentinvention;

FIG. 2 is a partial cross-sectional view taken along line 2—2 of FIG. 1;

FIG. 3 is one embodiment of a tool for use in a disc molding process forproducing an optical disc in accordance with the present invention;

FIG. 4 is a top view of one embodiment of the inner holder shown in FIG.3;

FIG. 5 is a cross-sectional view taken along line 5—5 of FIG. 4;

FIG. 6 is a partial cross-sectional view showing one embodiment of anoptical disc assembly for use in an optical disc storage system inaccordance with the present invention;

FIG. 7 is a partial cross-sectional view showing another embodiment ofan optical disc assembly in accordance with the present invention;

FIG. 8 is a partial cross-sectional view showing another embodiment ofan optical disc assembly in accordance with the present invention;

FIG. 9 is a top view of another embodiment of an inner holder inaccordance with the present invention;

FIG. 10 is a cross-sectional view taken along line 9—9 of FIG. 9;

FIG. 11 is a top view of another embodiment of an inner holder inaccordance with the present invention;

FIG. 12 is a cross-sectional view of an inner holder taken along line12—12 of FIG. 11;

FIG. 13 is a partial cross-sectional view of another embodiment of anoptical disc assembly in accordance with the present invention;

FIG. 14 is a cross-sectional view of another embodiment of an innerholder in accordance with the present invention; and

FIG. 15 is a partial cross-sectional view of an optical disc inaccordance with the present invention formed using the inner holder ofFIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an optical disc in accordance with the present invention isgenerally shown at 20. The optical disc may be a read only or a writableoptical disc, such as those previously described herein. The opticaldisc 20 is round or generally “disc shaped”, and may include an opening22 centrally located and extending therethrough. The optical disc 20includes a disc substrate 24, which includes an information area 26, anintermediate region 28 and a central portion 29. The intermediate region28 may be located between the information area 26 and the centralportion 29.

As previously described herein, data is stored within the informationarea 26 of the optical disc 20 as a series of lower reflectance “pits”bored within a plane of higher reflectance “lands”. The microscopic pitsmay be formed on the surface of the plastic disc during an injectionmolding process, which is described in detail further in thespecification. The pits on the optical disc are arranged in a spiraltrack originating at the beginning of information area 26, adjacentintermediate region 28, and ending at the disc outer edge 30. The spiraltrack can be defined as a plurality of generally concentric tracks,wherein each generally concentric track is a cycle of the spiral track.Alternatively, the information area 26 may consist of a plurality ofconcentric tracks. Similarly, for writable optical discs, such asmagneto optical discs or phase change optical discs, the data is encodedwithin the readable material arranged in a spiral track. In particular,the writable discs may include a spiral or concentric track formed inthe disc substrate, wherein the data is encoded in the writable materiallocated in the regions between the spiral track cycles.

The intermediate region 28 includes a disc alignment mechanism 32. Thedisc alignment mechanism 32 allows engagement or mating of the opticaldisc with an optical disc player (in particular, the drive spindlelocated within the optical disc player) for retention and rotation ofthe disc during operation of the optical disc player. Further, theconcentricity of the formatted information located within theinformation area 26 is specified relative to the disc alignmentmechanism 32. The disc alignment mechanism 32 serves as a disc alignmentfeature for centering an optical disc player drive mechanism to theformatted surface (information) on the disc (or more particularly, thegenerally concentric tracks).

In FIG. 2 a partial cross-sectional view of the optical disc 20 takenalong line 2—2 in FIG. 1 is generally shown. The disc substrate 24includes formatted surface 34 located within information area 26. In theexemplary embodiment shown, the disc alignment mechanism 32 may be anannular member or ring 36 generally concentrically located about opening22. Due to the alignment mechanism 32, it is not required that centerhole 22 be centered relative to the formatted surface 34. The annularring 36 extends as a molded projection from the surface of the opticaldisc 20. The height of the annular ring 36 relative to the discsubstrate 24 is preferably less than the thickness of the discsubstrate, and must be sized such that it is capable of being receivedor coupled to an optical disc player/drive spindle. In one preferredembodiment, the annular ring 36 extends at least 0.5 mm above thesurface of the disc substrate 24. Alternatively, it is recognized thatdisc alignment mechanism 32 may consist of a separately manufacturedpiece adhered to the disc substrate 24.

The concentricity of formatted surface 34 is specified relative toannular ring 36. Further, annular ring 36 is used for mating with thedrive spindle in an optical disc player during operation of the opticaldisc, and for centering the optical disc player drive mechanism to theformatted surface 34. It is recognized that disc alignment mechanism 32may be comprised of other features within the disc substrate 24 forregistration of the formatted surface 34. Further, it is recognized thatthe intermediate region 28 may include other indentations orprojections, such as groove 38, which may be formed within the opticaldisc 20 as a by-product of the disc molding process. In a conventionaldisc molding process, the resulting groove 38 is 0.3 mm or less deep andit is not shaped such that it is capable of being received by an opticaldisc player/drive spindle, and as such, is not capable in itself offunctioning as a disc alignment feature.

Further, it is also recognized that a member 40 may be secured acrossopening 22. In one exemplary embodiment, the member 40 is a metallicwasher secured over the opening 22 by an adhesive. The member 40 is notrequired for centering of the optical disc 20 formatted surface 34relative to a drive mechanism. The member 40 may be utilized as an aidfor magnetically coupling the optical disc 20 to an optical disc playerdrive spindle during reading/playing/writing of the optical disc.

Since the concentricity of the data on the optical disc 20 is registeredrelative to the disc alignment mechanism 32, and the disc alignmentmechanism 32 serves as a disc alignment feature for centering theoptical disc player drive mechanism to the data (or data tracks), theoptical disc 20 has a low RTIR error during reading of the disc. Thedata is not registered/centered relative to the disc opening 22.Further, since the optical disc 20 has a low RTIR error, a hub is notrequired for centering the optical disc 20 within an optical discplayer. It is recognized that the disc alignment mechanism 32 mayconsist of other means for coupling/mating with the optical disc player,and is preferably located adjacent the formatted surface 34.

In the exemplary embodiment shown, it is recognized that since the discalignment mechanism 32 (shown as annular ring 36) extends from the discsubstrate 24, the disc alignment mechanism 32 may also be used as astacking mechanism to aid in stacking a plurality of optical discs 20.When used as a stacking mechanism, the disc alignment mechanism 32provides a separation between each optical disc 20, and separates theformatted surface 34 from contact with an adjacent disc.

In one exemplary embodiment, the optical disc 20 in accordance with thepresent invention is a high capacity optical disc which includes a discsubstrate formed of a polycarbonate resin. The optical disc 20 may be aread only or writable optical disc. The disc 20 has an outside diameterof 130 mm, and includes opening 22 having a diameter of 15 mm. Theannular ring 36 is located 8.3 mm from the opening 22. The annular ring36 has a width of 1 mm and a height of 0.5 mm relative to the substratesurface. Groove 38 is located 9.6 mm from opening 22, having a width of0.9 mm and a depth of 0.3 mm. The formatted surface 34 is located 4.0 mmfrom annular ring 36, and 2.9 mm from groove 38.

In this exemplary embodiment, the optical disc 20 has a track pitch of0.35 μm, having an RTIR of 30 μm or less. The optical disc 20 may be ahigh-capacity optical disc, having a storage capacity greater than 20gigabytes.

In FIG. 3, a cross section of an optical tool for use in producing lowRTIR optical discs 20 is generally shown at 42. The optical tool 42 isused for molding replicas of the optical disc 20 in a disc moldingprocess, which can be similar to the disc molding process as previouslydescribed herein. The optical tool 42 is part of a complete optical discmolding manufacturing process (not shown), which can be a process formanufacturing CD-ROM, CVD, MO, or phase change optical discs, aspreviously described herein. The low RTIR optical tool 42 generallyincludes a fixed side 44 and a moving side 46. The fixed side 44 ismovably coupled to the moving side 46 to form a disc substrate cavity48. A sprue 50 is provided for allowing material for forming thesubstrate 24, such as a polycarbonate resin, to enter the disc substratecavity 48.

The moving side 46 includes a sprue eject 52, a gate cut 54, a producteject 56, a rod cover 58, an inner holder 60 and stamper 62. Sprue eject52 is utilized for ejection of sprue 50 during opening of the opticaltool 42. Gate cut 54 is utilized for cutting the opening 22 withinoptical disc 20. Product eject 56 is utilized for ejecting the finishedproduct replica optical disc 20 from the optical tool 42. Inner holder60 is removable for changing out and securing stamper 62. Rod cover 58is stationary within the moving side 46 to constrain the positions ofthe adjacent movable parts product eject 56 and the inner holder 60.Stamper 62 is utilized for forming the formatted surface 34 into opticaldisc 20. The stamper 62 includes data tracks. In an exemplaryembodiment, for CD-ROM the stamper 62 includes tracks formed of data andpits corresponding to the data to be embossed into the information area26 of the optical disc substrate 24 during the optical disc moldingprocess.

The process for molding a low RTIR optical disc 20 in accordance withthe present invention includes filling the disc substrate cavity 48 witha disc molding material, such as polycarbonate resin, through the sprue50 channel (indicated at 59). After the polycarbonate resin is forcedinto the disc substrate cavity, but before cooling of the polycarbonateresin, the gate cut 54 is operated forward, indicated by arrow 64, tocut opening 22 within the optical disc substrate 24. After cooling ofthe resin within the disc substrate cavity 48, the formatted surface 34has been embossed in optical disc 20, and the optical tool 42 is opened.The sprue eject 56 is operated forward (indicated by arrow 61). At thesame time, the product eject 56 is operated to remove or eject themolded disc substrate 24 from the optical tool 42 surface (specifically,the surface of the moving side 46). During this process, the rod cover58 remains stationary. The above process is repeated for the manufactureof each additional optical disc (or replica optical disc) substrate. Theoptical disc 20 then passes through a finishing process for formingadditional layers over the disc substrate, such as reflective orrecording layers, and in the case of CD-ROM protective layers, dependingon the type and use of the optical disc.

Referring to FIG. 4, a top view of the inner holder 60 is shown. Theinner holder 60 includes a body 63, a shape imparting mechanism 65 andlocking mechanism 66. The shape imparting mechanism 65 imparts a shapeto the optical disc substrate 24 and the locking mechanism 66 retainsthe stamper 62 within optical tool 42. In the embodiment shown, is theshape imparting mechanism 65 includes an annular depression 67, and thelocking mechanism 66 includes an annular raised portion 68. The innerholder body 63 is generally cylindrically shaped, and is preferablyformed of metal, such as stainless steel or aluminum. Referring to FIG.5, a cross-sectional elevational view of the inner holder 60 is shown.The inner holder 60 further includes a lock down ring 70.

The inner holder 60 is secured within the optical tool 42 at the lockdown ring 70. The inner holder 60 is removable from the optical tool 42for allowing the stamper 62 to be changed out. Once a different stamper62 is in place, the inner holder 60 is again secured to the optical tool42 at lock down ring 70. In a locked position, the locking mechanismraised portion 68 extends over an edge of the stamper 62, securelyretaining the stamper 62 in place.

In the exemplary embodiment shown, the inner holder 60 is utilized forforming the disc alignment mechanism 32 within the optical discsubstrate 24. The inner holder 60 raised portion 68 and depression 67are located along the top surface 72 of the inner holder 60. The shapeof the top surface 72 is reflected into the optical disc substrate 24during the disc molding process. Specifically, in the exemplaryembodiment shown, depression 67 corresponds to form the disc alignmentmechanism 32 shown as annular ring 36 and the raised portion 68 formsannular groove 38.

The unique optical tooling in accordance with the present inventionproduces an optical disc having a low RTIR. The stamper 62 is tightlyfitted to the inner holder 60. The concentricity of the formattedinformation stamped into the disc substrate 24 is specified by a singlemetal part, such as the inner holder 60. Since the concentricity of theformatted information is specified relative to the disc alignmentmechanism 32 formed by the inner holder 60, the introduction of RTIRerror into the optical disc is limited to the punching of the stamper 62and the formation of the master disc and subsequent formation of thestamper. Any debris from the gate cut action and any non-concentricityor misinstallation of the sprue eject 52, the gate 54, the product eject56, and the rod cover 58 no longer will add to the resulting RTIR errorstamped onto the optical disc 20.

The concentricity of the formatted surface 34 is now specified relativeto the disc alignment mechanism 32, and does not rely on other featuresof the disc, such as center hole or opening 22 or the use of a hub forcentering the optical disc 20 on an optical disc player drive spindle.The resulting disc alignment mechanism 32 is matable with the opticaldisc player drive spindle, wherein the concentricity of the formattedsurface 34 is specified relative to the disc alignment mechanism 32.Additional costly processes are no longer necessary for positioning andcentering a hub within the optical disc 20 opening 22 for centering theoptical disc 20 relative to the formatted surface 34 on an optical discplayer.

Referring to FIG. 6, an optical disc assembly 80 located on an opticaldisc player drive spindle 82, in accordance with the present invention,is generally shown. The optical disc assembly 80 includes cartridge 84,including cartridge shell 85, having the optical disc 20 containedtherein.

Optical disc player drive spindle 82 is generally cylindrically shapedand includes a top surface 88 having a spindle mechanism 90 for engagingor mating with the disc alignment mechanism 32 of the optical disc 20.In the exemplary embodiment shown, the spindle mechanism 90 includes anannular groove 92 which corresponds and mates with the annular ring 36of the optical disc 20. In one preferred embodiment, the spindlemechanism annular groove 92 is at least 0.55 mm deep relative to the topsurface of the drive spindle 82, and is shaped for mating with the discalignment mechanism 32. A central hub portion 94 may further extend fromthe top surface 88.

To read optical disc 20, the optical disc assembly 80 is inserted withinan optical disc player (not shown). The drive spindle 82 is operatedupward (indicated by directional arrow 96) to engage or mate with theoptical disc 20. In particular, the disc alignment mechanism annularring 36 is received within the spindle mechanism annular groove 92 forengagement or mating of the optical disc 20 to the optical disc playerdrive spindle 82 in the normal direction.

Additional means may be provided for retaining the optical disc 20against the drive spindle 82. In the embodiment shown, a mechanicalhold-down 86, secured to the top surface of cartridge shell 85 (such asby an adhesive) is utilized to apply a force normal to the surface ofoptical disc 20 for magnetic attraction (coupling) and trapping of theoptical disc 20 between the metallic member 86 and the drive spindle 82.

When the optical disc 20 is engaged with drive spindle 82, the centralportion 94 extends through the optical disc opening 22. Since theoptical disc 20 is engaged with the drive spindle 82 using discalignment mechanism 32 and spindle mechanism 90, the central hub portion94 is not used for engagement or registration of the optical disc 20. Assuch, there can be a loose fit between the central hub portion 94 andthe optical disc opening 22.

The concentricity of formatted surface 34 is specified relative toannular ring 36. Further, since annular ring 36 is used for mating withthe drive spindle 82, the formatted surface 34 is centered to theoptical disc player drive spindle 82. Therefore, the disc alignmentmechanism 32 both allows for engagement of the drive spindle 82 with theoptical disc 20 and for centering the drive spindle 82 to the formattedsurface 34.

In FIG. 7, another embodiment of low RTIR optical disc 20 coupled withinan optical disc player is generally shown in partial cross section at100 (the disc cartridge shell is not shown for clarity). Drive spindle82 includes a flange 102 extending radially from a drive spindle body104. Extending from flange 102 are disc contact members 106. When theoptical disc 20 is engaged within the optical disc player, drive spindle82 is operated upward to engage the optical disc 20. Additionally, anormal force is magnetically applied downward through the mechanicalhold down 86, further coupling the optical disc 20 between themechanical hold down 86 and the drive spindle 82. During engagement ofoptical disc 20, an outside edge 108 of the flange 102 is in precisefit/registration with the inside of annular ring 36. Further, disccontact member 106 is secured against the optical disc 20. Although thecentral hub portion 94 extends through the optical disc opening 22, thecentral hub portion 94 may be loosely fit within the optical discopening 22.

As previously described herein, the concentricity of the formattedsurface 34 (data tracks) is linked to the registration provided byannular ring 36 (formed by the inner holder 60 during the disc moldingprocess). Further, the concentricity of the formatted surface 34 on theoptical disc 20 is maintained by the precise fit of the drive spindleedge 108 with the optical disc annular ring 36.

Referring to FIG. 8, additional embodiments of the present invention aregenerally shown in partial cross-sectional view at 112, in which opticaldisc 20 is shown mated with drive spindle 82 (again, the disc cartridgeis not shown for clarity). The optical disc 20 disc alignment mechanism32 receives the spindle mechanism 90 for engagement of the optical disc20 with the drive spindle 82. In one embodiment, the disc alignmentmechanism 32 is an annular groove 116 and the spindle mechanism 90 is anannular ring 114. Alternatively, it is recognized that spindle mechanism90 may include a mounting pin 120 which is received by correspondingmounting holes 122 within the optical disc 20. Again, since theconcentricity of formatted surface 34 is registered with respect to thedisc alignment mechanism 32 and the spindle mechanism 90, the centralhub portion 94 may extend loosely through opening 22.

It is also recognized that other means may be provided for retaining theoptical disc 20 against the drive spindle 82. For example, drive spindle82 may further include vacuum openings 95, shown extending through theflange 102. The vacuum openings 95 are in fluid communication with avacuum system (not shown). The vacuum system applies a force in thenormal direction, for retaining/coupling the optical disc 20 against thedrive spindle 82.

Referring to FIG. 9 and FIG. 10, a second embodiment of an inner holderis shown as inner holder 160 for forming an annular groove 116 withinthe optical disc 20 during the disc molding process (shown in FIG. 8).FIG. 9 is a top view of inner holder 60, and FIG. 10 is across-sectional elevational view of inner holder 60. The inner holder 60includes annular projection 124, which corresponds to the annular ring116 formed within the optical disc 20. In one preferred embodiment, theannular projection 124 has a height of at least 0.5 mm relative to theinner holder top surface 72.

Referring to FIG. 11 and FIG. 12, a third embodiment of the inner holderis shown as inner holder 260. FIG. 11 is a top view of inner holder 260,and FIG. 12 is an elevational view of inner holder 260 shown in crosssection. In this embodiment, inner holder 260 includes registration pins126 for forming the mounting pin holes 122 within the optical disc 20(shown in FIG. 8).

Referring to FIG. 13, another embodiment of the RTIR optical disc 20 anddrive spindle assembly 82 is generally shown at 130. In this embodiment,it is recognized that the formatted surface 34 may be on the same sideof the disc 20 which faces mechanical hold down 86, with the drivespindle 82 located on an opposite side of the optical disc 20. In thisembodiment, mechanical hold down 86 includes coupling mechanisms 134,which can be similar to the spindle mechanisms 90 which have beenpreviously described herein, for mating or engaging the mechanical holddown 86 with the optical disc 20. The drive spindle 82 further includesa spindle pin 136 secured within opening 138 (such as by an adhesive).The spindle pin 136 extends from the drive spindle 82 and is securelytolerance fit to the mechanical hold-down 86 for coupling the drivespindle 82 to the mechanical hold-down 86. Further, the mechanicalhold-down may be mechanically coupled to drive spindle 82 usingtechniques as previously described herein. In operation, as drivespindle 82 is rotated, since mechanical hold down 86 is directly coupledto the drive spindle 82, the mechanical hold-down 86 is also rotated,for rotating optical disc 20.

In FIG. 14, a fourth embodiment of the inner holder is shown as innerholder 260. In this embodiment, the shape imparting mechanism 65 isformed integral the locking mechanism 66. As previously describedherein, the shape imparting mechanism 65 includes an annular raisedportion or ridge, and the locking mechanism 66 extends beyond a sidewall of the inner holder 360. The inner holder 360 is removable from theoptical tool 42 for allowing the stamper 62 to be changed out. In alocked position, the locking mechanism 66 extends over an edge of thestamper 62, securely retaining the stamper 62 in place. The shape of thetop surface 72 is reflected into the optical disc substrate 24 duringthe disc holding process. As such, in contrast to a conventional disclocking mechanism, the shape and size of locking mechanism 66 must besuch that it forms a shape or groove into the optical disc substrate 24which is capable of functioning as a disc alignment mechanism andcapable of mating with an optical disc player drive spindle. In onepreferred embodiment, the disc locking mechanism extends at least 0.5 mmabove the top surface 72 of inner holder 260.

In FIG. 15, one exemplary embodiment of an optical disc is shown, formedusing inner holder 260 in a disc molding process. The inner holder 260is utilized for forming the disc alignment mechanism 32 within theoptical disc substrate 24. The disc alignment mechanism 32 is replicatedinto the optical disc substrate 24 using the inner holder shapeimparting mechanism 65 which is formed integral the locking mechanism66. The resulting disc alignment mechanism 32 is shaped and sized suchthat it is capable of mating or coupling with an optical disc drivespindle, for centering the generally concentric data tracks on theformatted surface 34 on the drive spindle. It is also recognized thatthe shape imparting mechanism 65 may be formed as part of the discstamper, or from other disc molding parts. In one preferred embodiment,the disc alignment mechanism 32 has a depth of at least 0.5 mm relativeto the disc substrate 24 surface.

The hubless optical disc having a low radial runout in accordance withthe present invention is useful for very high capacity optical discs.The high density optical disc in accordance with the present inventionhas a low RTIR error which does not require the use of a hub forcentering the information on the disc. The high density optical disc maybe mounted and centered on features integrally molded onto the plasticsubstrate of the disc. With the present invention, optical discs havingan information capacity of 20 gigabytes or greater may be manufacturedand used due to the low introduction of RTIR error into the discsubstrate by utilizing the disc alignment mechanism for centering datatracks to a drive spindle, in accordance with the present invention.

Numerous characteristics and advantages of the invention have been setforth in the foregoing description. It will be understood, of course,that this disclosure is, and in many respects, only illustrative.Changes can be made in details, particularly in matters of shape, sizeand arrangement of parts without exceeding the scope of the invention.The invention scope is defined in the language in which the appendedclaims are expressed.

What is claimed is:
 1. A disc molding apparatus for forming an opticaldisc in a disc molding process, the disc molding apparatus comprising: adisc substrate cavity for forming a disc substrate therein; a spruemechanism in fluid communication with the disc substrate cavity forforcing disc molding material into the disc substrate cavity; aremovable stamper located on one side of the disc substrate cavity forforming formatted data into the disc substrate; an inner holderreleasibly mounted adjacent said removable stamper for releasiblylocking said removable stamper within the disc molding apparatus, theinner holder including a locking mechanism for retaining said removablestamper in the disc molding apparatus; and means for forming a discalignment mechanism in the disc substrate, positioned between theformatted data and a center of the disc substrate, wherein theconcentricity of the formatted data is specified relative to the discalignment mechanism, wherein the means for forming a disc alignmentmechanism includes the inner holder, wherein the inner holder includes ashape imparting mechanism located adjacent the locking mechanism forforming the disc alignment mechanism into the disc substrate.
 2. Thedisc molding apparatus of claim 1, wherein the shape imparting mechanismincludes an annular ring thereon.
 3. The disc molding apparatus of claim1, wherein the shape imparting mechanism includes an annular depressionlocated therein.
 4. The disc molding apparatus of claim 3, wherein theshape imparting mechanism includes the locking mechanism used forretaining said removable stamper within the disc molding apparatus.
 5. Adisc molding apparatus for forming an optical disc in a disc moldingprocess, the disc molding apparatus comprising: a disc substrate cavityfor forming a disc substrate therein; a sprue mechanism in fluidcommunication with the disc substrate cavity for forcing disc moldingmaterial into the disc substrate cavity; a removable stamper located onone side of the disc substrate cavity for forming formatted data intothe disc substrate; an inner holder releasibly mounted adjacent saidremovable stamper for releasibly locking said removable stamper withinthe disc molding apparatus, the inner holder including a lockingmechanism for retaining said removable stamper in the disc moldingapparatus; and means for forming a disc alignment mechanism in the discsubstrate, positioned between the formatted data and a center of thedisc substrate, wherein the concentricity of the formatted data isspecified relative to the disc alignment mechanism, wherein the meansfor forming a disc alignment mechanism includes the inner holder,wherein the inner holder includes a shape imparting mechanism forforming the disc alignment mechanism into the disc substrate, whereinthe shape imparting mechanism includes a plurality of registration pinsextending therefrom.
 6. A disc molding apparatus for forming an opticaldisc in a disc molding process, the disc molding apparatus comprising: adisc substrate cavity for forming a disc substrate therein; a spruemechanism in fluid communication with the disc substrate cavity forforcing disc molding material into the disc substrate cavity; aremovable stamper located on one side of the disc substrate cavity forforming formatted data into the disc substrate; an inner holderreleasibly mounted adjacent said removable stamper for releasiblylocking said removable stamper within the disc molding apparatus, theinner holder including a locking mechanism for retaining said removablestamper in the disc molding apparatus; and means for forming a discalignment mechanism in the disc substrate, positioned between theformatted data and a center of the disc substrate, wherein theconcentricity of the formatted data is specified relative to the discalignment mechanism, wherein the means for forming a disc alignmentmechanism includes a shape imparting mechanism for forming the discalignment mechanism into the disc substrate, wherein the shape impartingmechanism is located on said removable stamper.
 7. A disc moldingapparatus for forming an optical disc in a disc molding process, thedisc molding apparatus comprising: a disc substrate cavity for forming adisc substrate therein; a sprue mechanism in fluid communication withthe disc substrate cavity for allowing disc molding material into thedisc substrate cavity; a removable stamper located on one side of thedisc substrate cavity for forming formatted data into the discsubstrate; an inner holder releasibly mounted adjacent said removablestamper for releasibly locking said removable stamper within the discmolding apparatus, the inner holder including a locking mechanism forretaining said removable stamper in the disc molding apparatus; and amechanism separate from the locking mechanism for forming a discalignment mechanism in the disc substrate, positioned between theformatted data and a center of the disc substrate, wherein the mechanismincludes a shape imparting mechanism which extends at least 0.5 mm intothe disc substrate cavity, and wherein the concentricity of theformatted data is specified relative to the disc alignment mechanism. 8.A disc molding apparatus for forming an optical disc in a disc moldingprocess, the disc molding apparatus comprising: a disc substrate cavityfor forming a disc substrate therein; a sprue mechanism in fluidcommunication with the disc substrate cavity for allowing disc moldingmaterial into the disc substrate cavity; a removable stamper located onone side of the disc substrate cavity for forming formatted data intothe disc substrate; and an inner holder releasibly mounted adjacent saidremovable stamper for releasibly locking said removable stamper withinthe disc molding apparatus, the inner holder including a lockingmechanism for retaining said removable stamper in the disc moldingapparatus and a mechanism for forming a disc alignment mechanism in thedisc substrate, positioned between the formatted data and a center ofthe disc substrate, wherein the mechanism includes a shape impartingmechanism which extends at least 0.5 mm into the disc substrate cavity,and wherein the concentricity of the formatted data is specifiedrelative to the disc alignment mechanism; and wherein the shapeimparting mechanism is located on the locking mechanism.